The study described in this proposal is designed to develop a basis for understanding how drinking water becomes contaminated with carcinogenic, toxic compounds during the chlorination treatment process. It is now accepted that most of the contamination results from chlorination of the humic acids, which are trace impurities in the majority of water sources, but the reactions and intermediates that lead to the contamination are not well understood and relatively unexplored. The investigation will begin with the chlorination of model compounds, such as resorcinol, which simulate the aromatic substituents in the humic acids. Chlorinations will be conducted with NaOCl in CH3OH/H2O, a procedure which has recently been shown in (with resorcinol) to yield kinetic products and to pinpoint the structure of the intermediate that undergoes ring-opening. The study will be extended to other chlorinating agents such as NH2Cl and C102 and to the bromination of model compounds. Finally, using the data from the chlorination and bromination studies, an attempt will be made to further explore the structures of the humic acids. Fluorination reactions will also be applied to the study of the humic acids. Hopefully, a more complete, mechanistic understanding of the contamination process will suggest procedures for avoiding or controlling the problem during the treatment of drinking water.